In recent years, MIMO (Multiple-Input Multiple-Output) has received attention as a system for implementing high-speed transmission effectively using a frequency band limited in a radio communication technique. The MIMO is a technique for transmitting data using multiple antennas in both of transmitting and receiving. By transmitting various data from multiple transmitting antennas, a transmission capacity can be improved without expanding time and frequency resources.
Application of multiple code words (MCW: Multi Code Word) is effective as a data transmission method in the MIMO. In the multiple code words, after a CRC (Cyclic Redundancy Check) is assigned every data of each transmission path formed by multiple transmitting antennas or beams, an error correcting code such as a convolutional code, a Turbo code or an LDPC code is assigned and setting of a modulation and coding scheme (MCS) according to an SINR (Signal-to-Interference plus Noise power Ratio) corresponding to the appropriate transmission path (the transmitting antenna or beam) can be made. The flexible setting of the modulation and coding scheme can be made thus and moreover, error detection by the CRC can be performed every code word (CW) (every transmission path) in the multiple code words, so that a unit of retransmitting control can be set in a transmission path unit (a transmitting antenna or beam unit) and gain by the retransmitting control is obtained efficiently.
Here, the case of performing HARQ control using multiple code words in MIMO method as retransmitting control by hybrid-ARQ (Hybrid-Automatic Repeat reQuest) (hereinafter described as HARQ) in, for example, a cellular system for mobile communication such as a mobile telephone is considered. Here, the case of transmitting a signal from a radio base station (BS) used as a transmitting equipment (a transmitting station) to user equipment (UE) of a mobile station used as a receiving equipment (a receiving station) is illustrated. In this case, a pilot signal in a control channel, a control signal including multiple RV parameters disposed every code word, etc. are transmitted from the transmitting equipment to the receiving equipment. Also, Ack (Acknowledgement) or Nack (Negative Acknowledgement) every code word is transmitted as a response signal from the receiving equipment to the transmitting equipment.
FIG. 11 shows an operation example in HARQ control using multiple code words. A transmitting equipment (BS) respectively transmits transmission data data#1, data#2 to a receiving equipment (UE) in multiple code words CW1, CW2. In the receiving equipment, these transmission data data#1, data#2 are received and each of the data is decoded and Ack of the case where a received signal can be normally acquired or Nack of the case where a received signal has an error is transmitted to the transmitting equipment as a response signal every code word according to the availability of a decoding result. Here, the transmitting equipment retransmits data every code word when Nack is received from the receiving equipment. At the time of retransmitting, the receiving equipment respectively decodes the received retransmission data and synthesizes the retransmission data to the first received data (HARQ synthesis) every code word and transmits Ack or Nack to the transmitting equipment according to the right and wrong of the received data after synthesis.
In the HARQ synthesis for multiple code words as described above, the HARQ control is performed every code word, so that Ack/Nack feedback, Ack/Nack information, retransmission data of other code words, etc. cannot be utilized for Ack/Nack feedback, decoding, synthesis of the appropriate code word, etc. and energy used in retransmitting is wasted.    Non-patent Reference 1: 3GPP TSG RAN WG1 #42, R1-050912, Qualcomm Europe, “MIMO proposal for MIMO-WCDMA evaluation”, Aug. 29-Sep. 2, 2005